1. Field of the Invention
The present invention is generally related to the control of the air/fuel mixture in an internal combustion engine and, more specifically, to the control of the flow of inducted secondary air streams into the cylinders of the internal combustion engine in such a way that the overall effective air/fuel ratio is stoichiometric.
2. Description of the Related Art
Many different types of fuel control systems are know to those skilled in the art. As an example, U.S. Pat. No. 6,799,422, which issued to Westerbeke, et al. on Oct. 5, 2004, describes an emissions control. A method of controlling emissions from a fixed-speed internal combustion engine includes injecting a controlled flow of air into the exhaust between a first catalyst bed adapted to reduce HC and NOx emissions, and a second catalyst bed adapted to reduce CO emissions. The flow of air is controlled to optimize the level of CO emissions, preferably as a function of engine load or temperature. In a marine engine-generator set, the flow of air is controlled as a function of generator load or temperature of the exhaust mixture entering the second catalyst bed, and seawater is injected into the exhaust stream downstream of the catalysts.
U.S. Pat. No. 6,460,330, which issued to Yoshida et al. on Oct. 8, 2002, describes an engine intake air/fuel ratio control system in outboard engine system. In an engine intake air/fuel ratio control system in an outboard engine system, a secondary air passage for supplying secondary air for regulating the air/fuel ratio of an air/fuel mixture is connected to a carburetor in an intake system of an engine, and a duty control valve is connected to the secondary air passage. A duty control unit is connected to the duty control valve for controlling the duty ratio of a pulse applied to a coil of the duty control valve, and an LAF sensor is mounted to an exhaust system for detecting an air/fuel ratio of an exhaust gas to input a detection signal proportional to the air/fuel ratio of the exhaust gas to the duty control unit. Thus, in any of a case when the tolerance of the purifying rate of the catalytic converter is set relatively widely with an engine output taken into consideration to a certain extent, and a case when the set range is shifted to a rich side of the air/fuel ratio with the engine output taken into serious consideration, the air/fuel ratio of the exhaust gas can be controlled properly to a desired target value.
U.S. Pat. No. 5,546,919, which issued to Iida et al. on Aug. 20, 1996, describes an operating arrangement for a gaseous fueled engine. A feedback control system maintains an air/fuel ratio at a stoichiometric ratio by mixing air is with a gaseous fuel supply to the charge former. A manually controlled air bleed is incorporated to permit adjustment for deterioration in the system due to age or carbon deposits or the like. In addition, the feedback control position of the air bleed valve is memorized and the memorized value is utilized for control under some conditions when feedback control would not be appropriate such as for cold starting when the sensor is not at its operating temperature or upon the resumption of normal control after a fuel shut off during decell.
U.S. Pat. No. 5,425,232, which issued to Holtermann on Jun. 20, 1995, describes a marine propulsion device with means for supplying secondary air to catalytic converter. Disclosed is a marine propulsion device comprising a combustion chamber, an exhaust passage, an air pump and a three-way catalytic converter. The air pump pumps air into the exhaust passage at or immediately upstream of the catalytic converter. By this construction the internal combustion engine can be run slightly rich, but the catalytic converter will see a close to stoichiometric mixture so that the pollutants in the exhaust stream can be oxidized or reduced appropriately since the catalytic converter will be able to operate as a three-way catalytic converter.
U.S. Pat. No. 4,841,940, which issued to Uranishi et al. on Jun. 27, 1989, describes an air/fuel ratio control device of an internal combustion engine. The device comprises an electric air bleed control valve which controls the amount of air fed into the fuel passage of the carburetor so that an air/fuel ratio becomes equal to the stoichiometric air/fuel ratio. The degree of opening of the air bleed control valve is increased as an electric current fed into the air bleed control valve is increased. Fuel vapor is fed into the intake passages from the canister. When the electric current fed into the air bleed control valve is increased and reaches a predetermined upper limit due to the supply of purge gas, the current fed into the air bleed control valve is instantaneously increased by a fixed amount.
U.S. Pat. No. 4,593,663, which issued to Atago et al. on Jun. 10, 1986, describes a control apparatus for an internal combustion engine having a carburetor. The apparatus controls the air/fuel ratio of the air/fuel mixture supplied to the engine in the steady operating condition of the engine on the basis of predetermined data determined relative to the engine crankshaft rotation speed and intake vacuum and stored in a memory. A three-way catalyst purifies engine exhaust gases and an output signal from an oxygen sensor to the exhaust system is fed back for the control of the air/fuel ratio in the engine exhaust gases.
U.S. Pat. No. 4,363,209, which issued to Atago et al. on Dec. 14, 1982, describes an air/fuel control method and apparatus for internal combustion engines. It controls the air/fuel ratio of the fuel-air mixture supplied to the engine. The device also comprises a thermal reactor in which the exhaust gas from the engine is caused to undergo reaction with secondary air supplied to the reactor. It also comprises an oxygen sensor disposed in an exhaust gas passage between the reactor and three-way catalyst.
U.S. Pat. No. 4,121,546, which issued to Hattori et al. on Oct. 24, 1978, describes an air/fuel ratio adjusting apparatus for an internal combustion engine. The apparatus employs a gas sensor whose electric characteristic changes rapidly at near the stoichiometric air/fuel ratio so as to maintain the air/fuel ratio of mixture at any desired air/fuel ratio other than the stoichiometric one. A bypass valve is mounted in a bypass passage for supplying additional air to the portion of the carburetor downstream of its throttle valve.
U.S. Pat. No. 4,075,835, which issued to Hattori et al. on Feb. 28, 1978, describes an additional air control device. In controlling an amount of intake air of an internal combustion engine, an error due to the delay time between the time at which the air/fuel ratio changes in the intake system of the engine and the time at which a gas sensor in the exhaust system of the engine senses the changes is compensated. At least two delay factor detectors, e.g., an engine speed sensor and a pressure sensor control the driving and the stopping of the drive motor coupled to a control valve mounted in the additional air passage in the intake system to thereby adjust the amount of additional air supply.
U.S. Pat. No. 4,072,137, which issued to Hattori et al. on Feb. 7, 1978, describes an air-to-fuel ratio adjusting system for an internal combustion engine. The system comprises an additional air supply passage communicating with a carburetor of an internal combustion engine at the position downstream of its throttle valve, a control valve disposed in the additional air supply passage to vary the passage area thereof, and a percolation sensor for detecting percolation phenomenon of the fuel during idling operation of the engine. When the occurrence of a percolation phenomenon is determined in accordance with the output signal of the percolation sensor, the control valve is controlled in response to the output signal of an air/fuel ratio sensor, whereas the control valve is held in a predetermined valve position when there is no occurrence of percolation phenomenon during idling operation of the engine.
U.S. Pat. No. 4,046,118, which issued to Aono on Sep. 6, 1977, describes an air/fuel mixture control apparatus for carbureted internal combustion engines. Air/fuel mixture control apparatus for a carbureted internal combustion engine having air bleed and fuel supply passages comprises a detector for sensing pre-combustion data such as engine operating parameters and an exhaust gas sensor for providing post-combustion data. The pre-combustion data is used to control the fuel flow rate, while the post-combustion data controls the passage of air through the air bleed. The pre-combustion data minimize the delay from the instant of disturbance to the engine to the instant at which a response is observed.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
In many types of internal combustion engines, the internal configuration of an intake manifold and the shapes of its associated conduits connected to the cylinders of the engine result in an unequal and non-uniform distribution of the air/fuel mixture flowing from a carburetor toward the intake valves of the cylinders of the engine. As a result, each of the cylinders of the engine can receive a fuel-air mixture having a different air/fuel ratio than the other cylinders. This non-uniformity of air/fuel ratio at the intake valves of the cylinders can create a situation where a proper stoichiometric ratio is virtually impossible to achieve. As a result, the efficient operation of a catalyst, downstream from the cylinders, can be severely and adversely affected. It would therefore be significantly beneficial if the air/fuel mixture flowing into each of the cylinders can be maintained at a generally stoichiometric ratio throughout the operating range of the internal combustion engine.